Aviation or motor fuels



1951 D. A. HOWES ET AL AVIATION OR MOTOR FUELS Filed Jan. 29, 1948 3Sheets-Sheet l 55 00}. uuanmuaa uzruutm tau: 93mm uzbfiuu 5 0 0 W 8 8 BN m 6 SPECIFIC FUEL COHSUMPTlOH lb/BHP/HR INVENTORS DONALD ALBERT HOWES,THOMAS TAIT,

PATRICK DOCKSEY, STANLEY FRANCIS BIRCH,AND WILLIAM ARTHUR PARTRIDGE Nov.20, 1951 D. A. HOW-ES ETAL 2,576,071

AVIATION OR MOTOR FUELS Filed Jan. 29, 1948 s Sheets-Sheet 2.

VIII! INVENTORS DONALD ALBERT HOWES, THOMAS TAIT, PATRICK DOCKSEY,STANLEY FRANCIS BIRCH, AND WILLIAM ARTHUR PARTRIDGE Nov. 20, 1951 D,HQWES g 2,576,071

AVIATION OR MOTOR FUELS I Filed Jan. 29, 1948 3 Sheets-Sheet 5 INVENTORSDONALD ALBERT HOWES, THOMAS TAIT,

PATRICK DOCKSEY, STANLEY FRANCIS BIRCH, AND WILLIAM ARTHUR PARTRIDGE s2,WA M Maw.

Patented Nov. 20, 1951 2,576,071 AVIATION on MOTOR FUELS Donald AlbertHowes, Thomas Tait, Patrick Docksey, Stanley Francis Birch, and WilliamArthur Partridge, Sunbury-on-Thames, England, assignors to Anglo-IranianOil Company Limited, London, England, a British joint-stock corporationApplication January 29, 1948, Serial N 0. 4,974 In Great BritainFebruary 24, 1941 6 Claims.

.normal butenes or propene, or hydrogenated copolymers of isobutene andnormal butenes. Tetraethyl lead is then added to the blend inproportions prescribed by aviation fuel specifications, which areusually 3-6 ccs. per imperial gallon.

The octane number of such fuels normally determined according to amethod such as the C. F; R. Motor Method is not actually a trueindication of anti-knock or power output chemo-- teristics of a fuel,particularly at rich fuel air mixture strengths. This is made clear inthe following Table 1, in which octane numbers determined by the C. F.R. Motor Method with respect to six samples of fuel of known compositionand characteristics are set beside equivalent numbers that representactual peak performance tests made in a standard engine unit underidentical test conditions, the engine being coupled to a water brake andcooled by an air stream from an electrically driven fan and operatedunder the following conditions:

Compression ratio, 8:1

Speed, 2400 R. P. M.

Cylinder head temperature, 185 C.

Inlet air temperature, 110 C.

Ignition advance, 29

Table 1 Relative Peak Power output at rich mixture strength in an aircooled aeroengine in percentage as compared with a standard fuel 1 G. F.R. Motor Octane Fuel Sample No.

Per cent 1 The standard fuel was isooctaue to which had been added 1.25cc. E. L. per U. 8. gallon.

thetemperatures at the required values.

The tests are carried out in the following manner:

The engine which is first warmed up and then adjusted to the standardconditions of the test and the fuel to be tested is thereupon passedinto a tank in the determined quantity for the test, such as 10-20gallons.

The inlet manifold pressure which is controlled bya compressor orsupercharger is adjusted to a low value (generally atmospheric or justover), and the carburettor adjusted so that the air-fuel ratio is slowlyincreased until slight detonation is heard, while adjusting the brakeloading to keep the speed constant, and adjusting the inlet air heatingand wind speed in order to maintain The engine is then run under theseconditions for a few minutes while the operator. satisfies himself thatit is on the point of slight detonation, that is when detonation is justaudible.

The fuel supply is then changed to a graduated burette and the fuelconsumption measured by an observer by timing with a stop watch, theconsumption of /2 or 1 pint of fuel. At the same time another observernotes the brake loading in pounds and from this. reading calculates thepower output of the engine in terms of brake horse power (B. H. P.) andalso brake mean effective pressure (B. M. E. P.) lb./sq. in. Knowing thespecific gravity of the fuel, the specific consumption is thencalculated as lb./B. H. P./hr. This value is then plotted against B. M.E. P. at slight knocking. The process is then repeated at increasinginlet manifold pressures up to and just beyond the maximum power outputof the engine on the particular fuel, thus obtaining a curve ofperformance (B. M. E. P.) against specific consumption at slight audibleknock.

A similar curve is also obtained at the same time for a standardreference fuel against which the aviation fuel under test may becompared. In most cases the standard reference fuel is one known fromgeneral experience to be fully satisfactory under all flying conditionsand used as a minimum acceptance standard of performance. Thus in Figure1 of the accompanying drawing Fuel A would be considered a satisfactoryfuel, whereas Fuel B would be considered unsatisfactory. A convenientnumerical index for the engine performance of the fuel in terms of thestandard reference fuel is obtained by expressing the maximum B. M. E.P. given at the peak of the curve (Figure 1) by the fuel under test, asa percentage of that given by the standard reference fuel at the peak ofthe curve. Thus. if the standard reference fuel as in Figure 1, gives apeak B. M. E. P. of 210 lb./sq. in., and Fuel A gives a peak a. M. E. P.of 21-7 Ila/sq. in., a may be regarded as having a relative rating, ascompared with the reference fuel, of 103%. Similarly Fuel B which has apeak B. M. E. P. of 189 lb./ sq. in., may be regarded, as having arelative rating of 90%.

It is found in practice that when straight run distillates produced fromnaphthenic crude oils are used in aviation fuels as blends withsynthetic isoparailinic materials such as those hereinbefore referredto, the blends are satisfactory as to power output characteristics whenthey contain 50-60% by volume of the synthetic isoparaffln component. Onthe other hand, when straight run distillates from paraffinic crude oilsare used, aviation fuels of 100 octane number that are prising thecyclic hydrocarbons and branched chain hydrocarbons boilingapproximately in the range 72 C. to 92 C. to the substantial exclusionfrom the fractions recovered of n-pentane, nhexane and n-heptane andheavier hydrocarbons when containing -substantial proportions ofaromatic hydrocarbons.

Aviation gasoline fraction or fractions Heavier hydrocar bonsSnperfractionation B. P. 300 C.

Isopentane isohemne isoheptane cut cut out n-pentone n-hcxanc n-betoneand cut out has er hydrocarbons Solvent mnem l iip. mt .DistllationLow grade material Amati 100 O. N. SPIRIT with satisfactory with respectto power output characteristics, can only be prepared by using a'greater quantity of the synthetic isoparaflin component the cost ofwhose production is greatly in excess of the cost of producing straightrun distillates. Proportions of from 70% to 90% of the syntheticisoparaffln component are normal when such distillates are used forblending. Thus the proportion of the isoparaflinic component required isdependent on the aero-engine antiknock value of the straight runcomponent. The

is determined by the proportion of the isoparaffinic material used.

a The invention has among its objects to produce high grade aviation ormotor fuels from straight run distillates of mineral oils, underconditions of economy, by avoiding or minimising the use as blendingcomponents of the moreexpensive synthetic isoparaflin materials, .and'

mainly or entirely to use straight run distillates or fractions thereof.

In carrying the invention into effect in the use of a paraffin basecrude Iranian mineral oil, the crude oil is distilled for the productionof a fraction or fractions boiling within the aviation gasoline range,said fraction or fractions being superaddition of Tetra-ethyl lead 40The n-heptane fraction together with heavier hydrocarbons may be subjectto, solvent extraction and the rafiinate produced may be added to then-pentane and n-hexane fractions, while the I extract may be distilledand the aromatic hydrocarbons boiling in the motor spirit rangeseparated by fractionation.

The aromatic hydrocarbons separated maybe further treated for theirconcentration before use and may be used for addition to fractionsrecovered under conditions of superfractionation. It s however preferredto add to the mixture of the isopentane and isohexane and isoheptanefractions respectively containing the hydrocarbons of high octane numberhereinbefore set forth, a proportion of toluene or other aromatichydrocarbon or hydrocarbons boiling in the motor spirit range.

The removal from the gasoline distillate of the normal paraflins,pentane, hexane and heptane or any of them or fractions rich in suchnormal paraflins may be by effective superfractionation under theconditions hereinafter described, without substantial loss of high gradematerial, whereby a substantial improvement is cftested which in generalincreases the octane rating of the blended fuel produced in the use ofthe high-grade fractions recovered from the distillate to allow octanenumber aviation fuels to be obtained by the mere addition to the dis-7gtillate of up to 3 to 6 ml. tetra-ethyl lead fluid 7 column having afractionation efficiency equiv- 5. alent to that of '75 theoreticalplates whereby yields result from initial boiling point to 92 C. thatare set out in the table.

Table 2 Cd! (Pentunc Isomers) Isopentane (a) N -pentane IrohezanwFraction (b) 3-Methylpentane. N -Hexane "Isoheptanfl Fradion (c)Methylcyclopentane Benzene 2.2:Dimethylpeniane. 2.4-DimethylpenianeCyclohexanc 2.2.3-Trimethylbutanc l-Metbyl-2-is0propyl-cyclopropane..-3.3-Dimethy1pentane IJ-Dimethylcyclopentane 2-Methylhexane-;1.3-Dimethylcyclopentane trans LzDimethylcyclopentane 3-Methylhexane3-Ethylpentane N -Hepta bi i WMOQ QO:

assess lsooctane, 1 cc. '1. E. L.

obtained, other materials being present in only very small amounts, forexample 1-3% by volume.

contamination of the fractions with hydrocarbons of closely relatedboiling points and low octane number is so minimised that neither theoctane number of the fuel produced, nor its freedom from detonationunder normal or peak power output conditions are substantially affected.

The boiling ranges of the high octane number fractions separated mayvary according to the composition of the crude oils employed and be soadjusted as to include the valuable mate- In the case of the so-calledIsohexane" fraction it is found possible when dealing with Iranian crudeoil to recover a fraction having for example a boiling range of from 45C. or lower to about 64 C., but precision in fractionation is necessaryto ensure that the fraction contains little n-pentane (B. P. 36 C. O. N.(C. F. R. M.) 61) and also little n-hexane (B. P. 68.8 C. O.N. (C. F. R.M.) 25).

In the case of the so-called Isoheptane fraction, it is found possibleto recover a fraction having a boiling range of 72 C. to about 92 C.,and in this case also precision in fractionation is necessary to ensurethat while the fraction contains as much methylcyclopentane (B. P. 72 C.O. N. (C. F. R. M.) 82), as possible, and as little n-hexane as possibleat the lower .end of its boiling range, and as much dimethylcyclopentanes and as little 3-methyl hexane (B. P. 91.8 C. O. N. -(C. F.R. M.) ca. 45) and 3-ethyl pentane (B. P. 93.3 C. O. N. (C. F. R. M.)ca. 45) as possible at the higher end of its boiling range. It ishowever not possible even under the conditions of superfractionationdescribed to effect complete segregation of low and high octane numberfractions. For example, owing to the pecular vapourliquid relationshipof mixtures of n-hexane and benzene it is frequently found that then-hexane rials of high octane number, and to avoid those of low octanenumber, under the conditions of substantial precision of fractionationindicated.

The aromatic hydrocarbons present in the crude oil may also beconcentrated by effective fractionation and used in such restrictedproportion as is permitted by aviation fuel specifications. In generalhowever, owing to the formation of constant boiling point mixtures,benzene is distilled at a temperature lower than its normal boilingpoint and in the Near Eastern crude oil referred to boils over the range69 to 77 C. Thus a certain amount of benzene is segregated in then-hexane fraction, and the bulk of it recovered in the iso-heptanefraction.

The process of the invention is illustrated by way of example in Figure2 of the accompanying diagrammatic drawing which illustrates afractionating plant in which fractionation according to the inventionmay be carried out after first preparing two basic fractions forsubmission to fractionation for the separation of the normal paraffinhydrocarbons and isopentane and for the separation of the isohexane and"isoheptane fractions, these latter fractions comprising hydrocarbonsrespectively having 6 and 7 carbon atoms in the molecule and of nearlyrelated boiling points and high octane numbers. Figures 3 and 4illustrate other modifications.

In carrying the invention into effect as illustrated in Figure 2, thecrude oil is first treated for preparation from it of two basicfractions. For this purpose the crude oil is fed by pump from a storagetank I (Figure 2) by way of a pipe line 2 to a continuous flashdistillation unit a, 1) comprising a primary flash column a having theequivalent of 20 theoretical plates operating at a reflux ratio of 2:1,a pressure of 40 lbs/sq. in., an overhead temperature of for exampleabout 95 C. and a bottom temperature of mout 235 C. The secondary'columnbof the unit a, b is provided with the equivalent of 24 theoreticalplates, and operates at a reflux ratio of 4:1, at atmospheric pressureand at an overhead temperature for example of about 98 C.

and a bottom temperature for example of about 263 C. In operation thecrude oil enters the primary flash column a and a light fraction boilingfor example up to 69 C. together with the lighter gaseous components aretaken overhead. The overhead fraction under these conditions consists ofhydrocarbons having 1 to 6 carbon atoms asi'aotr 7 in the molecule. Thisfraction. is hereinafter referred to as the primary flash distillate.

The residue leaving the column it passes to the secondary column b ofthe unit a, b by way of the pipe line 3, whereby an overhead productboiling for example substantially below 120 C. may

be obtained.

The overhead product from the column I: thus consists of hydrocarbonshaving 6. carbon atoms in the molecule, that were not taken overhead inthe column 0, together with hydrocarbons of higher boiling point up toand including normal hydrocarbons having 7 carbon atoms in the molecule.This fraction is hereinafter referred to as the "isoheptane basefraction. v

The primaryv flash distillate from fractionating column a. is passed bythe pipe line 4 to a stabiliser column having the equivalent of 80theoretical plates. A reflux ratio of 4:1 may be maintained in thefractionating column 0, a pressure of 300 lbs/sq. in., an overheadtemperature for example of 46 C. and a bottom temperature 7 complishthis operation the column d may have the equivalent of 30 theoreticalplates, and may operate at a :1 reflux ratio and at about 100 I lbs/sq.in. pressure, with an'overhead temperature for example of 43.3 C. and abottom temperature of 121 C., whereby a. bottoms product substantiallyfree of butanes is ensured without loss of. isopentane. The eflluent,consisting of normal butane and isobutane from the fractionating columnd is taken overhead through pipe line 8 to storage. The debutanisedproduct leaving the base of the column d through the pipe line 1 passesto the superfractionating column e, which may have the equivalent of 50theoretical plates, in which ,a reflux ratio of :1, 9. pressure of 10lbs/sq. in.-

an overhead temperature of 54.5" C., and a normal bottom temperature offor example 103.75'"

C. may be maintained. I

The operating conditions in the column e are so determined that theresidue leaving the bottom of the column contains a normal pentaneconcentrationsuch that the isohexane" overhead fraction from column 9contains not more than 3%. It is necessary however to ensure thatsubstantially all the cyclopentane and dimethylbutane available remainsin the bottoms product from column e, which is accomplished bypermitting a small amount of normal pentane also to be present.

The cyclopentane-dimethylbutane content of the overhead from thesuperfractionating column e is thus determined by distillation of a 100ml. sample to 10% residue in a plate laborato y fractionating column at:1 reflux ratio. This 10% residue is re-distilled to dryness in a. flaskon a water bath, and the refractive index of the distillate determined,from which the cyclopentane-dimethylbutane content of ,the originalsample of overhead is easily estimated.

The fractionation operation carried out in the superfractionating columne results in the pro- 8 auction of two tractionuhamely the pentanefraction overhead, and the "hexane'? fraction as a bottoms product.These fractions are passed to the superfractionating columns I and arespectively for the separation as overhead products of isopentane fromcolumn I and isomeric branched hexanes and cyclopentane from column a.

The overhead from the superfractionating column e is passed through apipe line I as feed to the superfractionating column I, which isprovided with the equivalent of 50 theoretical plates. and may operateat a pressure or 10 lbs/sq. in. at a reflux ratio of 15:1, an overheadtemperature of 42.2" C. and a bottom temperature of 51.8 0.. whereby thefeed may be separated into an isopentane fraction overhead containingnot more than 3% normal pentane, taken through the pipe line "to storageand a normal pentane bottoms that is withdrawn through the pipe line H.

The bottoms product from the super-fractionating column e is passed bypipe line I! as feed to the superfractionating column '0 which has theequivalent of 50 theoreticalplates and operates at atmospheric pressureand with a reflux ratio of 15:1, at an overhead temperature of 655 C.and at a bottom temperature of 873 C., yielding an isohexane" fractionoverhead taken to storage through the pipe line It and normal hexanebottoms which through the pipe line I4. Separation between these twofractions may thus be so determined as to yield an overhead "lsohexanefraction of octane number between 77 and 81 (C. F. R. Motonllethod). Ahigh yield may be obtained'when operating for the production of a loweroctane number product, and the separation made whereby there is nonormal hexane in the overhead, but the bottoms contain a certain amountof ii-methylpentane.

This type or "isohexane" fraction contains no normal hexane and iscomposed of:

' 4 Octane No. 3% n-pentane (governed by column e) All cyclopentane 83All 2.2-dimethylbutane 96 All 2.3-dimethylbutane 95 All 2-methylpentane'73 And approximately all 3-methylpentane '15 In the "isohexane fractionan'upper limit of 2% of normal pentane and 1% of normal hexane should beregarded as the maximum limit of impurity, representing a drop of oneoctane number (calculated) "Isohexane fractions of higher octane numberbut obtainable with lower yields may be produced by leaving largerquantities ofthe 3- and z-methylpentanes in the bottoms. The control ofthe operation to-obtain a product of this type i may be made so that thehexane fraction fed to the column is split in an overhead/bottoms ratioknown by trial to give the desired octane number and yield.

Analytical control of the separation for maximum ield of material of thelowest octane number may be made by distilling the isohexane" fractionoverhead in a 25 plate laboratory column Analytical control of theseparation for yields of products of higher octane number may be made bchecking the cut points of the products obtained from the two boilingpoint curves determined in a 25 plate laboratory column, for example ifthe foregoing test shows the presence of a substantial proportion ofnormal hexane, suitable control adjustments may be made.

The "Isoheptane base-fraction recovered as overhead from the secondarycolumn b of the crude oil distillation unitmay be passed through thepipe line I to a superfractionation column it having the equivalent of50 theoretical plates, operating at atmospheric pressure at a refluxratio of 15:1, an overhead temperature of 605 C. and bottom temperatureof 933 C. The overhead taken at this column consists of normal hexanetaken off through the pipe line I6 and the conditions may be sodetermined that the maximum quantity of methylcyclopentane and theminimum quantity of normal hexane remain in the" bottoms.

Analysis of the bottoms for normal hexane and methylcyclopentane may bemade by the distillation of a sample to 85 C. in a 25 plate laboratorycolumn at a reflux ratio of 20:1. The distillate to 85 C. may bere-distilled to 75 C. in a 25 plate laboratory column at 30:1 refluxratio. This fraction may be composed of a mixture of benzene,methylcyclopentane and normal hexane, and may be analysed for theseconstituents by absorption of the benzene in sulphuric acid anddetermination of the ratio of naphthene to paraffin in the aromatic freespirit by the linear relationship between the specific refractions ofthe two components.

The bottoms product resulting from the operation carried out in thesuperfractionation column h are passed through a pipe line I! to asuperfractionating column i in which a separation is made between the"isoheptane" fraction and the normal heptane fraction that are withdrawnthrough the pipe lines l8 and I9 respectively. This separation may beaccomplished by providing in the column the equivalent of 50 theoreticalplates and operating under atmospheric pressure at a reflux ratio of10:1, overhead temperature of 83.8 C. and bottom temperature of 101.25C. The operation may be carried out so that no more than 0.5% of normalheptane remains in the overhead. The n-heptane fraction together withheavier hydrocarbons when containing substantial proportions of aromatichydrocarbons may be subjected to solvent extraction instead of beingwithdrawn from the system through the pipe line Hi. In such case thefraction in whole or in part may be conducted through valved pipe line2| to a combined solvent extraction and refining unit 60 22 from whichthe rafiinate produced may be withdrawn through the pipe line 23 and thearomatic hydrocarbons boiling in the motor spirit range withdrawnthrough the pipe line 24 following their distillation from the extractin the extraction unit 22.

The combined operationscarried out in the superfractionating column hand i may be controlled so that the resulting isoheptane fraction hasthe following properties:

(a) Distilling to 75 C. not less than 17.5% weight.

(b) Distilling to 85 C. not less than 44.0% weight.

(0) Normal hexane content of fraction to 75 C.

not more than 20% weight.

10 (d) Fraction above 95 0. not more than 0.5%

weight. (e) Fraction distilling to 85 C. should contain not less than40% to 75 C. sothat not more than distills between 75 0. and 85 0.

Under the conditions of the example described there are produced thefollowing high grade fractions suitable for blending together or withother high grade materials for the production of an aviation or motorfuel of high octane number, that is to say:

(i) Isopentane as overhead from the superfractionatin column I, to thesubstantial exclusion of normal pentane.

/ (ii) An isohexene fraction as overhead from the superfractionatingcolumn g having an approximate boiling range of 45 C.-64.- C. includingcyclopentane and the four hexane isomers, to the substantial exclusionof normal hexane.

(iii) An isoheptane fraction as overheadfrom the superfractionatingcolumn 2', having an approximate boiling range of 72 C.92 C.

Such separated fractions of high G. F. R.

motor octane number may be blended together in determined proportions toyield aviation fuels having satisfactory power output characteristicsand of high rating as determined by performance in a standard engineunit in the manner hereinbefore described. Tetra-ethyl lead fluid isadded in amounts prescribed by specification, for example 3-6 ml. perimperial gallon.

It will be understood that the ratio of the constituents of a blend mayvary widely and may comprise a number of fractions boiling in thegasoline range that have been recovered from straight run distillates inthe manner hereinbefore described, in addition to which there may be aproportion of an aromatic hydrocarbon or hydrocarbons such as benzene,toluene or xylene added as may be necessary to meet specificationrequirements.

1 With regard to proportions, that of isopentane is limited by reason ofits high vapour pressure, but it may be present in such proportion notex- 45 ceeding 20% by volume of the finished blend as is 0 cas of astraight blend of the three fractions,

where A, B, C, D,

the proportion of isohexane fraction should not exceed 25% by volume butwhereother hydrocarbon blending materials are used, the proportion ofisohexane fraction may amount to as much as 35% by volume. Also, whereother hydrocarbon blending materials are used, the proportion of theisoheptane fraction should not exceed 55% by volume, while when bothsynthetic isoparafiins and aromatic hydrocarbons are used as blendingmaterials, the proportion of the isoheptane fraction should not exceed40% by volume.

In the preparation of any aviation fuel blend from fractions produced inthe manner hereinbefore described there may be included other high gradematerials boiling in the gasoline range.

The proportions may be determined as follows:

Aa+Bb+CO+Dd 5:100:12

ard engine unit as hereinbefore described. The

. are volume percentages.

Component A' 25% Engine performance No. 80 Component B, Engineperformance No. 95 Component C Engine performance No. 100 Component D45% Engine performance No. 75

then within thefnormal limits of experimental error, the correspondingnumber of the blend is given by the equation:

(X80) (10x95) 20 x100 45 75) 83.25say 83 In blending the constituents ofaviation fuels 4 to meet the. requirements of a specification, it ispossible on knowing the engine performance numbers of the blends todetermine by simple inspection which of the blends meets thespeciflcation. Small quantities of such blends may then be prepared andexamined in the laboratory forconfirmation, and any slight adjustment ofblend composition may then be made experimentally, and the blendcomposition finally determined. In applying this usual method ofblending aviation and motor fuels it is necessary also to bear in mindeconomic considerations by using as little as may be suflicient ofexpensive materials and as much as may be satisfactory of inexpensivematerials, utilising such materials as are actually available andleaving a minimum unutilised surplus. Thus the fractions obtained "bysuperfractionation under the conditions of the process of the inventionmay be adjusted both in quantity and quality to meet specificationrequirements.

The following are examples of suitable blends:

Example 1 Percent by volume Isopentane 20 "Isohexane fraction 10Isoheptane fraction 50 Toluene 20 This blend, after the addition of 4ml. tetraethyl lead fluid per imperial gallon, satisfies therequirements of current 100 octane number avi ation fuel specification,and has satisfactory power output characteristics in both air cooled andwater cooled aero-engines at all air/fuel mixture ratios.

V Example 2 Percent by volume Isopentane 10 Isohexane fraction v 20Isoheptane fraction '70 Composition, Vol. Per Cent Alkylate 30 30 20Houdry Cat. Cracked Gasoline 38 28 20 Isopentane l5 16 12 ParaflinlcGasoline... l7 Naphthenic Gasoline. 2? lsohexane C 22 Isoheptane Cut 20o Estd. Octane No 100.7 100.9 100 Estd. Rel. Peak Pegasus Performance105 105.6 106 Emmple 7 Composition, Vol. Per Cent Hydroeodimer 4E 33Fluid Cat. Cracked Gasoline.- l8 l5 Isopentane 1 3 10 7o ParaflinicGasoline l2 N8 hthenic Gasoline 22 Iso exane Cut---. 25 Isoheptane C l7Estd. Octane N0 100 100 '100' Estd. Rel. Peak Pegasus Performance 105. 5106 107 Example 3 1 Percent by volume Isopentane 10 Isohexane fraction20 Isoheptane fraction 50 Aromatic extract 20 with the addition of 4 ml.tetra-ethyl lead fluid per imperial gallon this blend gave satisfactoryperformance in an aero-engine under all mixture conditions and showed arelative peak performance of 98%.

Example 4 Percent by volume Isopentane 10 Isohexane" fraction 2t)Isoheptane fraction 40 Aromatic extract With the additon of 4 ml.tetra-ethyl lead fluid per imperial gallon this blend also had arelative peak performance of 103%.

Example 5 The following example is a blend of octane number aviationfuel by blending an alkylate being the product of the alkylation ofisobutane with an oleflne reactant in the presence of concentratedsulphuric acid.

Per cent by volume Isopentane 10 Isohexane fraction 20 Isoheptanefraction 25 Alkylate (93 octane number) 45 When tested with the additionof 4? ml.-tetraethyl lead fluid per imperial gallon, this blend also hada relative peak performance of 100%.

The following Examples 6-10 illustrate the Example 6 NaphtbenicGasoline-- Example 8 Composition, Vol. Per Cent Hot Acid Octane FluidCat. Cracked Aromatic Fractio Ispeniane.--; Pareflinic Gasoline; Nahthenic Gasolinc Iso exane Cut." lsoheptane CuL.

Estd. Octane No Estd. Rel. Peak Pegasus Performance Example 9Composition, Vol. Per Cent Naphthenic Gasollnot. Isohexane CutIsoheptane Cut Estd. Octane No; Estd. Rel. Peak Pegasus PerformanceExample 10 Composition, Vol. Per Cent Alkylatc Aromatic Extract.Isopentane Paraiiinic Gasoline Isohexane Cut Isoheptane Cut Estd. OctaneNo Estd. Rel Peak Pegasus Performance .i

The invention is applicable in the use of any crude mineral oil fromwhich a straight run distillate boiling in the aviation or motor spiritrange may be produced from which low grade fractions are removed in themanner described, and from which a series of high grade fractions arederived for blending together to produce a homogeneous high grade spiritto which may be added on aromatic or naphthenic hydrocarbon orhydrocarbons boiling in the aviation or motor spirit range together withthe prescribed proportion of tetra-ethyl lead fluid to yield a producthaving an octane number (0. F. R. Motor Method) in excess of 95.

The boiling range of the high grade and the low grade fractions may bedetermined according to the character or composition of the crude oilfrom which the fractions are derived, the range of the high gradefractions being so determined as to include the respective fractionsproduced according to the process of this invention, while the boilingrange of the low grade fractions separated from the distillate are sodetermined as to include the corresponding normal paraffins.

Since the number of constituents in any one of the fractions may belarge, the calculation of optimum reflux ratio may be practicallyinconvenient. Thus a continuous operating column may be used undervarying conditions and particularly with varying reflux ratios, and theoptima conditions of operation may thus be determined by actual smallscale trial. Thus for example in order to determine the most suitablereflux ratio trial runs may be made at reflux ratios between for example10:1 and 50:1 and the products analysed. The lowest reflux ratio thusdetermined under which a satisfactory product is secured is obviouslythe economic one for use in the fractionating columns of the industrialplant.

Instead of applying the process of the invention to two basic fractionsproduced in a flash column, the process may be applied to a singlefraction or other number of selected fractions to yield isopentane,isohexane and isoheptane fractions and for the segregation therefrom oflow grade material including the normal paraffin hydrocarbons.Furthermore, no limitation is imposed to the reflux ratios, pressure andtemperature conditions and the number of plates in the respectivecolumns.

The fractionation columns may be equipped in known manner for heatingthe feed, as for example by a pipe still; and each of the fractionatingcolumns e, 'f, g, h, i, may be provided at the base with a re-boiler bywhich heat may be supplied and the required temperature conditionsmaintained. Heat exchangers may also be employed for utilisation of thesensible heat of the effluents in known manner and pumps provided on thepipe lines adapted for control, whereby the determined reflux ratios maybe maintained and the determined proportions of the overhead productspass to storage. The equipment of the columns may conform to modernpractice, while the actual equipment of the plant is suchas is requiredto carry out the superfractionation in the columns under the processconditions hereinbefore described. No limitation is however involved tothe fractionation of the two basic distillates.

The process of the invention may be applied to a single distillatesubjected to superfractionation in series flow through the fractionatingcolumns. Thus the stabilised and debutanised distillatemay pass inseries through fractionating columns such as e, f, g, h, and i Fig. 3,whereby the isopentane and normal pentane leave the column e as overheadand pass to the cloumn f, and the isohexane" fraction and higherhydrocarbons leave the column e as bottoms and pass from the column e toa mid-position in the length of the column 9. while isopentane leavesthe column 1 as overhead and normal pentane as bottoms. Thus theisohexane fraction leaves the column g as overhead and normal hexane andhigher hydrocarbons as bottoms, the latter passing to the column hwhence normal hexane leaves as overhead and the isoheptane fractionincluding higher hydrocarbons as bottoms pass to the column i, fromwhich the "isoheptane fraction leaves as overhead and. the residue asbottoms. Thus the overhead from the columns I, g, and i (Figure 3) arethe same respective high grade fractions as from the columns ,f. g and iin the process described with. reference to Figure 2. 0r again thedebutanised feed may be passed in series through five superfractionatingcolumns 7, k, l, m, and n as illustrated in Figure 4, the top and bottomtemperatures in the columns being controlled as in the process describedwith reference to Figures 2 and 3. The first column 7' (Figure 4) servesfor the separation of isopentane as overhead and the second column Itserves for the separation of n-pentane as overhead. The conditions ofoperation of the remaining columns I, m, and n (Figure 4) correspondwith the conditions in the columns 9, h and i of Figures 2 and 3. Thusthe operations are so determined in the columns 1', is, Z, 112. and n(Figure 4) that isopentane, n-pentane, the "isohexane fraction, n-hexaneand the isoheptane fraction respectively leave as overhead, whilen-pentane and higher hydrocarbons, isohexane and higher hydrocarbons,n-hexane and higher hydrocarbons, isoheptane and higher hydrocarbons andthe residue respectively leave the same columns as bottoms. Theoperating conditions in the columns in carrying out the processaccording to themodification illustrated in Figure 4 are determinedaccording to the composition ofthe feed to the respective columns in themanner hereinbefo're described with reference to cording'ly. Furthermorethe high grade frac-' tions consisting of isopentane, the isohexanefraction and the 'isoheptane fraction are advantageously recovered asoverhead from the respective columns. It will however be understood'th'at' the actual fractionations effected in the respective columns maybe determined otherwise than as indicated respectively in Figures 2, 3and 4' to yield the high grade fractions referred to and 'for theseparation of the respective normal hydrocarbons under control to ensureprecision of fractionation in the columns.

1'6 is necessary to ensure the req [red volatility of the blend, saidisohexane fraction being added in a proportion not exceeding 25% byvolume of the finished blend up to the limit of vapour to liquid ratiounder which vapour lock is/ avoided and said isoheptane" fraction beingadded in such proportion as to constitute substantially the remainder ofthe blend. v

2. A process for the production of a blended high grade aviation ormotor fuel having an engine performancenumber at least substantiallyequal to that of iso-octane blended with 1.25 c. c. o

of T. E. L. fluid per U. S. gallon as a minimum standard of performancewhich comprises blending an isopentane fraction consisting of substan-,tially pure isopentane, an isohexane" fraction having a boiling rangeof 45-64 C., and an iso- No limitation is involved to the process con-'ditions particularly indicated as these may be varied according toanalysis and preliminary laboratory and other tests made for the purposeof determination oi. the most advantageous proc- -be separated in thecourse of the distillation for utilisation as such in the mannerhereinbefore described.

This'application is a continuation-in-part of 2 our co-pendingapplication No. 428,530, filed January 28, 1942, now abandoned.

. I We claim:

l. A process for the production of a blended high grade aviation ormotor fuel having an engine performance number at least substantiallyequal to that'of iso-octane blended with 1.25 c. c. T. E.' L. fluid perU. S. gallon as a minimum standard of performance which comprisesblending an isopentane fraction consisting of substantially pureisopentane, an isohexane fraction having a boiling] range of -64 C., anisoheptane fraction having a boiling range of from 72 C. to about 92 C.together with a proportion of tetra ethyl lead fluid not exceeding 6cos. per imperial gallon, said fractions being present each insignificant amount to produce a finished blend of the stated engineperformance number and being derived from the distillation of a straightrun petroleum distillate obtained from paraflinic crude and boiling inthe aviation or motor spirit range under conditions of precision infractionation'including the use of not substantially less thantheoretical plates and a reflux ratio ,of not substantially less than10:1, said isopentane fraction being added in such proportion not exceeding 20% by volume of the finished blend as heptane fraction having aboiling range of from 72 C. to about 92 C. together with at least onearomatic hydrocarbon blending material and a proportion of tetra ethyllead fluid not exceeding 6 ccs. per imperial gallon, said fractionsconstituting the major portion of the finished blend, being present eachin significant amounts to produce a finished blend of the stated engineperformance number and being derived from the distillation of a straightrun petroleum distillate obtained from paraffinic crude and boiling inthe aviation or motor spirit range under conditions of precision infractionation including the use of not substantially less than 50theoretical plates and a reflux ratio of not substantially less than10:1, said isopentane fraction being added in such proportion notexceeding 20% by volume of the finished blend as is necessary to ensurethe required volatility of the blend, said isohexanefraction being addedin a proportion not exceed-'- ing 35% by volume of the finished blend upto the limit of vapour to liquid ratio under which vapor lock isavoided, and said isoheptane fraction being added in a proportion notexceeding by volume of the'finished blend to constitute with saidaromatic hydrocarbon blending material substantially the remainder offinished blend.

3. A process according to claim 2 for the production of said aviation ormotor fuel in which aromatic hydrocarbons and synthetically preparedisoparaflins constitute the aromatic hydrocarbon blending' material andin which said isoheptane fraction is added in a proportion not exceeding40% by volume of the finished blend. 4. A process according to claim 2in which the "isohexane fraction comprises not more than 3% n-pentane,cyclopentane, the four hexane isomers and substantially no n-hexane. 5.A process according to claim 2 in which the isohexane fraction comprisesnot more than 2% n-pentane, cyclopentane, the 'four hexane isomers andnot more than 1% n-hexane.

6. A process according to claim 2 in which the I DONALD ALBERT HOWES.THOMAS TAI'I.

PATRICK DOCKSEY.

STANLEY FRANCIS BIRCH. WILLIAM ARTHUR PARTRIDGE.

(References on following page) 17 18 REFERENCES CITED OTHER REFERENCESThe following references are of record in the Hubner et al., The Oil andGas Journal, Mar. file of this patent: 31, '1933, pp. 103-112.

UNITED STATES PATENTS Smittenberg et 2.1., Octane Ratings of a Num-Number Name Date 5 her of Pure Hydrocarbons and some 01 their BinaryMixtures, Journal of Institute 01 Pe- 2,204,215 Greensfelder June '11,1940 troleum VOL 26 1940 294 303 2,249,461 Diwoky July 15, 1941 pp2,305,026 Munday Dec. 15, 1942 2,407,717 Marschner Sept. 17, 1946 102,409,157 Schulze Oct. 8, 1946

1. A PROCESS FOR THE PRODUCTION OF A BLENDED HIGH GRADE AVIATION ORMOTOR FUEL HAVING AN ENGINE PERFORMANCE NUMBER AT LEAST SUBSTANTIALLYEQUAL TO THAT OF ISO-OCTANE BLENDED WITH 1.25 C.C. T. E. L. FLUID PER U.S. GALLON AS A MINIMUM STANDARD OF PERFORMANCE WHICH COMPRISES BLENDINGAN ISOPENTANE FRACTION CONSISTING OF SUBSTANTIALLY PURE ISOPENTANE, AN"ISOHEXANE" FRACTION HAVING A BOILING RANGE OF 45-64* C., AND"ISOHEPTANE" FRACTION HAVING A BOILING RANGE OF FROM 70* C. TO ABOUT 92*C. TOGETHER WITH A PROPORTION OF TETRA ETHYL LEAD FLUID NOT EXCEEDING 6CCS. PER IMPERIAL GALLON, SAID FRACTIONS BEING PRESENT EACH INSIGNIFICANT AMOUNT TO PRODUCE A FINISHED BLEND OF THE STATED ENGINEPERFORMANCE NUMBER AND BEING DERIVED FROM THE DISTILLATION OF A STRAIGHTRUN PETROLEUM DISTILLATE OBTAINED FROM PARAFFINIC CRUDE AND BOILING INTHE AVIATION OR MOTOR SPIRIT RANGE UNDER CONDITIONS OF PRECISION INFRACTIONATION INCLUDING THE USE OF NOT SUBSTANTIALLY LESS THAN 50THEORETICAL PLATES AND A REFLUX RATIO OF NOT SUBSTANTIALLY LESS THAN10:1, SAID ISOPENTANE FRACTION BEING ADDED IN SUCH PROPORTION NOTEXCEEDING 20% BY VOLUME OF THE FINISHED BLEND AS IS NECESSARY TO ENSURETHE REQUIRED VOLATILITY OF THE BLEND, SAID "ISOHEXANE" FRACTION BEINGADDED IN A PROPORTION NOT EXCEEDING 25% BY VOLUME OF THE FINISHED BLENDUP TO THE LIMIT OF VAPOUR TO LIQUID RATIO UNDER WHICH VAPOUR LOCK ISAVOIDED AND SAID "ISOHEPTANE" FRACTION BEING ADDED IN SUCH PROPORTION ASTO CONSTITUTE SUBSTANTIALLY THE REMAINDER OF THE BLAND.